Ammonium nitrate explosive composition

ABSTRACT

An explosive composition is provided which contains a distinct particulate ammonium nitrate phase and a distinct aqueous phase saturated with ammonium nitrate.

United States Patent Inventors Joseph R. Hradel Mount Pleasant, Micln;

Harold E. Staadt, Tulsa, Okla.

Apr. 21, 1969 Dec. 28, 1971 The Dow Chemical Company Midland, Mich.

Original application Jan. 5, 1959, Ser. No. 784,881. Divided and thisapplication Apr. 21, 1969, Ser. No. 818,087

Appl. No. Filed Patented Assignee AMMONIUM NITRATE EXPLOSIVE COMPOSITION13 Claims, No Drawings US. Cl 149/21, 149/40, 149/41, 149/43, 149/44,149/60, 149/112 Int. Cl C06b l/04 Field of Search 149/21, 40,

References Cited UNITED STATES PATENTS Hradel et al.

Taylor Streng et a1 Cook et a1. Staadt Hradel et a1. Hradel et a1.

Cook et a1. Grifi'lth Primary Examiner-Benjamin R. Padgett AssistantExaminer-Stephen .1, Lechert, Jr.

AllomeysGriswold & Burdick, Bruce M. Kanuch and William R. Norris 149/21X 149/21 X 149/21 X [49/21 X ABSTRACT: An explosive composition isprovided which contains a distinct particulate ammonium nitrate phaseand a distinct aqueous phase saturated with ammonium nitrate.

AMMONIUM NITRATE EXPLOSIVE COMPOSITION This is a division ofapplication, Ser. No. 784,88 1 filed Jan. 5, 1959.

it has been a desideratum in the explosives art to formulate andcompound explosive compositions which are easily and safely loaded intoa borehole or fissure in an earth formation which are of relatively lowcost and which do not produce toxic substances on detonation.

Accordingly, it is an object of this invention to provide an ammoniumnitrate explosive mixture in the form of an aqueous composition whichmay be readily loaded as by pumping the composition into a borehole orby first placing the composition, if pasty, in rigid or flexiblecontainers and positioning the containers in a borehole, the aqueouscomposition having substantially no voids therein and especially when inthe form of a slurry the composition further filling any confining spacein the manner of a liquid so as to generally eliminate voids below thesurface of the slurry.

It is another object of the invention to provide an ammonium nitrateexplosive composition which can be prepared from low cost materials.

It is another object of the invention to provide an ammonium nitrateexplosive composition compounded from substances which do not producetoxic products when the composition is detonated.

lt is a further object of the invention to provide an ammonium nitrateexplosive composition which is readily compounded at or near the sitewhere it is used.

These and other objects are attained upon admixing ammonium nitrate andwater in suitable proportions, hereinafter described, whereby there isobtained a paste or slurry of particulated ammonium nitrate in itssaturated aqueous solution.

The compositions of the invention may be compounded by first preparingan aqueous solution of ammonium nitrate from water and any grade ofammonium nitrate such as fertilizer grade ammonium nitrate or explosivesgrade ammonium nitrate, and slurrying therein or mixing therewith aparticulated ammonium nitrate. However, a most economical procedure isthat of admixing a particulated ammonium nitrate with one of the aqueousammonium nitrate solutions of commerce such as an aqueous solutioncontaining about 84 percent of ammonium nitrate as obtained in themanufacture of ammonium nitrate.

While a fine particulate grade of ammonium nitrate may be used to obtaina composition with somewhat greater work potential, it is generally moreeconomical to use an inexpensive grade such as fertilizer grade ammoniumnitrate in either prilled or granular form and, if necessary, toincrease the size of the load slightly. However, though a relativelycoarse grade of ammonium nitrate may be employed a grade of ammoniumnitrate having more than about 5 percent of particles of a size greaterthan that passing about a IO'mesh sieve (U.S. Sieve Series) is to beavoided as decreasing the sensitivity of the composition to initiationto an undesirably low level.

The components of the inventions may be combined in pro portions varyingfrom about 75 to 97 percent by weight of ammonium nitrate and from about3 to 25 percent by weight of water to produce a pasty to pumpable twophase composition, one of the phases being solid ammoniumnitrate, theother an aqueous solution saturated with respect to ammonium nitrate. Itis to be understood'that while compositions in this range will underroom temperature conditions contain both dissolved ammonium nitrate andsolid phase particulate ammonium nitrate, the relative amount ofammonium nitrate in each phase is determined by the temperature of themixture under equilibrium conditions. At higher temperatures more solidparticulate ammonium nitrate will be taken into solution that at lowertemperatures.

While such an aqueous composition of ammonium nitrate explosive isdetonable upon initiation by a suitably heavy initiator, it is generallyto be preferred that the slurry be admixed with up to about 35 percentby weight of a sensitizer to increase sensitivity as well as workpotential. In this instance the composition comprises up to 35 percentby weight of a sensitizer, 40-97 percent by weight of ammonium nitrate,a portion of which is in particulate form, and 3-25 percent by weightwater containing dissolved ammonium nitrate. Suitable sensitizersinclude light metals such as magnesium and magnesium-base alloyscomprising at least percent of magnesium, and aluminum and aluminum-basealloys comprising at least 80 percent of aluminum, the light metal beingin particulated fonn. Atomized pellets of light metal as well as theground flake form of metal may be used in compounding the explosivecomposition of the invention. Examples of suitable magnesium-base alloysinclude those having the ASTM designations ZKlO, ZK60, A241, as well asAZll containing 1 percent of manganese, ZK60 containing 2 percent ofthorium, and an alloy containing 2.8 percent of aluminum, 8.4 percent ofzinc, the balance magnesium. While the particulated metals may be usedin the form of ground or flaked particles a desirable form is that ofatomized pellets, for example, atomized metal pellets obtained asdescribed in U.S. Pat. Nos. 2,699,576 and 2,728,107.

Ground metals as produced are generally quite varied in particle sizeand usually contain a substantial amount of fines passing a 325 meshsieve. Not only are these fines rather easily ignited in air but theycontribute to low level initiation of particulate ammonium nitrate inadmixture therewith. Such fines are thus unsuitable in the preparationof relatively insensitive ammonium nitrate explosive mixtures. Groundmetals may be used upon separating the fines as by screening andselecting particles about percent of which are retained on a 140 meshsieve and not more than 1 percent of which pass a 200 mesh sieve. It isalso desirable to reject coarse metal particles not passing a 20 meshsieve as these are too large to react effectively during the briefinterval of the detonation reaction of ammonium nitrate, though thepresence of a small percent of larger particles does not particularlyadversely affect detonability of an ammonium nitrate explosive mixture.

On the other hand atomized metal pellets produced according to the U.S.patents referred to above are readily formed in a narrow range ofparticle sizes with little fines. While the same limits of metalparticle sizes generally apply whether the metal is ground or pelletizedthe following is a sieve analysis of a suitable pelletizedmagnesium-base alloy having the ASTM designation ZK60.

Other suitable sensitizers for the present explosive composition includefinely divided carbon, preferably passing a 325 mesh sieve, and mixturesof carbon and the above-mentioned particulate light metals. It is to bepreferred that the carbonparticulate metal mixtures contain at least 50to 75 percent by weight of the particulate metal.

Additional sensitizers which may be used include such inorganic salts aspotassium nitrate, sodium nitroprusside, potassium ferrocyanide,ammonium chromate, potassium nitrite, strontium nitrate, sodium cyanide,calcium nitrate and-ammonium hypophosphite all of which contain nitrogenand exhibit a melting point or decomposition point above a temperatureof C. These inorganic sensitizers are best employed in' the explosivecomposition of the invention in the range of about l5 to 35 percent byweight of the total composition.

If desired the explosive composition of the invention may be thickenedupon admixing therewith from about 0.1 to 5 petcent based on the weightof the liquid phase. of a thickening agent such as methyl cellulose orgum karaya. Other suitable thickening agents are carboxymethylcellulose, kava kava gum, guar gum, accroides gum, locust bean gum,balsam tolu form of atomized pellets. The particle size of theparticulated aluminum was such that about 0.4 percent was retained on a40 mesh sieve. about 85 percent was retained on 200 mesh sieve and about0.9 percent passed a 325 mesh sieve.

natural, lrish moss, Iceland moss and high molecular weight 5 Theprepared mixtures were loaded into individual shallow polyacrylarnide.boreholes drilled in clay soil and having a diameter of 4 inchesCompositions of the invention containing from about 3 w and a depth ofabout 4 feet. Successive boreholes were spaced 12 percent of water aregenerally possessed of a pastelike con- 9 20 feet p r The loading ofeach hole was accomsistency and are more conveniently loaded intoaccessible Phshad y first P g an "humor the form of a shaped b h lcharge armed with a blasting cap in the bottom of the hole andCompositions of the invention containing from about l2 to i the leadWires of the blasting Cap to firing 90mm] 25 percent ofwater aregenerally pumpable as a slurry and are switch. Each shaped charge wasused and posltroned w1th the useful in loading inaccessible orhorizontal or upwardly slop- Jet end ans facing "P q Y- ing borehoes' IThe explosrve m xtures contained 1n the plastic bags 1n In preparing anddewnafing the composition of the New which they were mixed were placedin respective testholes, the bag in each case deforming so as to coverthe mrtrator. tron, the ingredients of the composition are m1xedtogether in Sand was used as a tamp, the hole being filled from the bagto small quantities as by kneadmg in a plast1c bag or in larger groundlevel with sand. Detonation of the mixture was atquantrtres as wrth amechamcal agitator or paddle mixer. A

tempted by closrng the firing switch thus setting off the initiaload orcharge of the so-prepared mixture is placed in the tor at the bottom ofthe hole. In a comparison test 1n the form desired location, usually 1nthe confinement of a borehole. A 8 char 6 Such as a [former containin achar 6 of of a blank, one hole was loaded solely with :1 l0 poundquantil m l J t Pi l t 5 th ty of fertilizer grade of ammonium nitrateand an initiator.

l d q z i l 'g g h e The magnitudes of the detonations obtained weredeteranneN i ap mined by measuring the size of the crater produced.While the i ecmc m astmg P s aped a crater size alone is not indicationof the amount of earth for- F'f resin to e exploswe lo 1 i mation thatis broken up or loosened, it does give an indicamus f meted toward the fy f The tion of the work potential of the mixture detonated. The craterelecmcal lead from blasting cap ngged w a 9" size herein reported showshow much material was thrown suff f mechan'sm to a remote comm!ficiently so as not to fall back over the test hole. Test condil a sand9' 813W] p p h over the load tions and results are summarized in thetable 2. f lhmawf- The load 15 fired "P semhg 03' the blast In order tocompare the composition of the invention with .i s e h 8 A conventionalexplosives varied amounts of 60 percent The h p f f Invention P paredand d nat d dynamite each with a No. 8 Electric Blasting Cap therefor asdescribed is especrally advantageously used in nunmg were placed inshallow test holes 4 feet deep, tamped with operations m which the useof low cost compositions combinsand and detonated. Five pounds ofdynamite so loaded and ing the properties of good heave or workpotential with lower detonated produced a crater 5 feet in diameter and1.5 feet range bnsance and low toxicity istobedesired. deep; 10 poundsof dynamite produced a crater 8 feet in To demonstrate the properties ofthe ammonium explosive diameter and 1 foot deep; while 25 pounds ofdynamite mixture of the invention, various embodiments of theinvenproduced a crater ll feet in diameter and 5 feet deep. The tionwere prepared and tested. In each test a ID or a 25 pound results of theblank, Test No. 15, show the ammonium nitrate quantity of explosivemixture was formulated of a particulated alone is not detonable underthese conditions.

TABLE 2 Indicator Composltion Wel ht of Blasting Wt. ol RDX ln Craterdlmenslons. ft. FOAN. Hi0, Al. loa lbs. cap No. shaped charge, percentpercent percent 02. Diameter Depth Test N0 10 s 3125 3.. B5 7.5 1.5 10 s3.25 6 4.5 4... 1o 15 15 10 s 3.25 6 s 5.. so 10 1o 10 s 3.25 5 1. 5a... 15 a0 10 s 3.25 s a 7... so 25 15 10 s 3.25 s 4 a... s7 3 10 15 s 112 3 1;... s5 5 10 25 s 1 12 3 10. so 10 10 25 s 1 12 3 11... 9o 5 5 10s 3. 25 10 4 12... 75 5 20 10 s 3.25 10 6 1a... 70 a 21 10 s 3. 25 10 514... so 5 35 10 s s. 25 10 o 15 100 10 s 1.15

I Heaved and cracked. 3 it. 1 Temp only.

NOTE.-FGAN =fertlllzer grade of ammonium nitrate; RDX =trlmethylenetrlnitramlne.

fertilizer grade ammonium nitrate and water, with or withoutparticulated aluminum metal, in the proportions and amounts shown in thetable. The individual proportions were in each case mixed in a separatepolyethylene plastic bag of sufficient size to readily hold the quantityprepared. The various components of the mixture were weighed into thebag, the bag closed and the contents mixed together by kneading the bagwith the hands. The fertilizer grade ammonium nitrate contained about0.7 percent of wax, 1 percent of diatomaceous earth and 0.3 percent ofchalk. The particle size of the ammonium nitrate was such that 94percent by weight of the particles passed a 20 mesh sieve and 85 percentby weight were retained on a 100 mesh sieve. The aluminum metal was inthe In an additional test an explosive load weighing about 4 pounds andhaving the composition 50 percent of ammonium nitrate, 20 percent ofwater, and 30 percent of particulated aluminum was used to fill a 3 inchby 12 inch steel pipe nipple which was capped on both ends and laid onthe ground. The

I. An explosive composition comprising a particulate ammonium nitratephase in admixture with an aqueous solution phase saturated with respectto ammonium nitrate, particulate metal sensitizer and a thickening agentfor the aqueous solution phase.

2. The composition of claim 1 wherein the thickening agent comprisesfrom about 0.1 to about 5 percent by weight of the composition based onthe weight of the aqueous phase.

3. The composition of claim 1 wherein water comprises from about 3 toabout 25 percent by weight of the composition.

4. The composition of claim 1 including in addition at least oneadditional inorganic salt containing nitrogen.

5. The composition of claim 1 including in addition at least oneinorganic salt selected from the group consisting of potassium nitrate,sodium nitroprusside, potassium ferrocyanide, ammonium chlorate,potassium nitrate, strontium nitrate, sodium cyanide, calcium nitrate,or ammonium hypophosphite.

6. The composition of claim 1 including in addition an inorganicsensitizer.

7. The composition of claim 1 wherein the particulate metal sensitizeris a light metal.

8. The composition of claim 7 wherein the particulate metal sensitizercomprises up to about 35 percent by weight of the composition.

9. The composition of claim 1 wherein the particulate metal comprises alight metal selected from the group consisting of magnesium, magnesiumbase alloy, aluminum, aluminum base alloy or mixtures thereof.

10. The composition of claim 1 wherein the thickening agent comprises atleast one compound selected from the group consisting of methylcellulose, gum karaya, carboxymethyl cellulose, kava kava gum, guar gum,accroides gum, locust bean gum, balsam tolu natural, Irish moss, Icelandmoss, or high molecular weight polyacrylamide.

11. The composition of claim 1 wherein not more than about 5 percent byweight of the particulate ammonium nitrate are of a size greater thanthat passing a 10 mesh sieve.

12. An explosive composition comprising from about 40 to abut 97 percentby weight of a particulate ammonium nitrate phase, from about 3 to about25 percent by weight of an aqueous solution phase saturated with respectto ammonium nitrate, from 0-35 percent of particulate metal sensitizerand from about 0.1 to about 5.0 percent by weight based on the amount ofwater, of a thickening agent dispersed therein.

13. The composition as defined in claim 11 containing at least oneadditional inorganic salt containing nitrogen and having whichever isthe lowest of the melting point and decomposition point above about 100C.

2. The composition of claim 1 wherein the thickening agent comprisesfrom about 0.1 to about 5 percent by weight of the composition based onthe weight of the aqueous phase.
 3. The composition of claim 1 whereinwater comprises from about 3 to about 25 percent by weight of thecomposition.
 4. The composition of claim 1 including in addition atleast one additional inorganic salt containing nitrogen.
 5. Thecomposition of claim 1 including in addition at least one inorganic saltselected from the group consisting of potassium nitrate, sodiumnitroprusside, potassium ferrocyanide, ammonium chlorate, potassiumnitrate, strontium nitrate, sodium cyanide, calcium nitrate, or ammoniumhypophosphite.
 6. The composition of claim 1 including in addition aninorganic sensitizer.
 7. The composition of claim 1 wherein theparticulate metal sensitizer is a light metal.
 8. The composition ofclaim 7 wherein the particulate metal sensitizer comprises up to about35 percent by weight of the composition.
 9. The composition of claim 1wherein the particulate metal comprises a light metal selected from thegroup consisting of magnesium, magnesium base alloy, aluminum, aluminumbase alloy or mixtures thereof.
 10. The composition of claim 1 whereinthe thickening agent comprises at least one compound selected from thegroup consisting of methyl cellulose, gum karaya, carboxymethylcellulose, kava kava gum, guar gum, accroides gum, locust bean gum,balsam tolu natural, Irish moss, Iceland moss, or high molecular weightpolyacrylamide.
 11. The composition of claim 1 wherein not more thanabout 5 percent by weight of the particulate ammonium nitrate are of asize greater than that passing a 10 mesh sieve.
 12. An explosivecomposition comprising from about 40 to abut 97 percent by weight of aparticulate ammonium nitrate phase, from about 3 to about 25 percent byweight of an aqueous solution phase saturated with respect to ammoniumnitrate, from 0-35 percent of particulate metal sensitizer and fromabout 0.1 to about 5.0 percent by weight based on the amount of water,of a thickening agent dispersed therein.
 13. The composition as definedin claim 11 containing at least one additional inorganic salt containingnitrogen and having whichever is the lowest of the melting point anddecomposition point above about 100* C.